Field of the Invention
The present invention relates to an image processing apparatus, an image processing method, and a storage medium.
Description of the Related Art
According to conventional technology, a luminance signal and a chroma signal included in a video signal are transmitted as having different resolutions. In a standard definition (SD) video and a high definition (HD) video that use interlaced scanning, a signal format called “422 format” is often used to transmit the signals. The 422 format is a format in which two pixels' worth of a red chrominance signal and two pixels' worth of a blue chrominance signal are stored with respect to four pixels' worth of a luminance signal, and in this format, the chrominance signals have a resolution half that of the luminance signal. This is to save the signal bandwidth required for transmission and recording by utilizing the fact that the vision characteristics of human eyes are more sensitive to luminance changes, and relatively insensitive to color changes.
In recent years, ultra-high definition (UHD) videos with 4 k resolution and super-high vision (SHV) videos with 8 k resolution are beginning to be distributed through broadcasting and media. These signal formats use sequential (progressive) scanning, and a format called “420 format” is dominantly used. The 420 format is a format in which there are only one pixel's worth of a red chrominance signal and one pixel's worth of a blue chrominance signal with respect to four pixels' worth of a luminance signal, the four pixels including two pixels in the vertical direction and two pixels in the horizontal direction. In this case, the chrominance signals have a resolution half that of the luminance signal in the vertical and horizontal directions, which is equal to one quarter resolution in total.
The 420 format as described above is effective to save the bandwidth required for transmission and recording. However, many image processing operations simultaneously use the luminance signal and the chrominance signals. Examples of such image processing operations include color correction processing and tone correction processing that use a 3D look-up table, and the like.
In order to perform such image processing operations, it is necessary to adjust the resolution to match between the luminance signal and the chrominance signals. In order to adjust the resolution, usually, a method is used in which the resolutions of the chrominance signals are increased by pixel interpolation so as to match the resolution of the luminance signal. Alternatively, a method may be used in which image processing is performed by scaling down the luminance signal so as to match the resolution of the chrominance signals, and thereafter super-resolution processing is performed. Once image processing is performed by scaling down the luminance signal as described above, even when super-resolution processing is performed, the resolution information is not accurately restored, resulting in degradation of images.
Japanese Patent Laid-Open No. 2010-263598 discloses a method in which separate processing operations are performed on the luminance signal and the chrominance signals that have been processed to have a matching resolution. In the configuration disclosed in Japanese Patent Laid-Open No. 2010-263598, sharpness processing is performed on the luminance signal, separately from gain processing performed on RGB signals.
However, the conventional configuration has the following problems.
In order to perform image processing, such as color correction processing and tone correction processing, that use a 3D look-up table, it is necessary to adjust the resolution to match between the luminance signal and the chrominance signals. If processing is performed by increasing the resolution of the chrominance signals through pixel interpolation, the operating frequency bandwidth (processing load) of circuits required for the image processing increases.
In the configuration of Japanese Patent Laid-Open No. 2010-263598, the luminance signal and the RGB signals are processed separately, but the RGB signals have the same resolution as that of the luminance signal, and thus the required operating bandwidth also increases.
The problem that it is necessary to increase the operating bandwidth for image processing to be higher than the frequency bandwidth of the input signal arises when a hard circuit for image processing is used, and in image processing that uses a computer, the problem appears as an increased processing time.
Also, the problem arises not only in a signal in the 420 format, and is common in signals in the 422 format and the 411 format in which the luminance signal and the chrominance signals have different resolutions.
In order to solve the problem, the present invention provides a technique for performing image processing on an input signal composed of a plurality of image component signals having different resolutions so as to not compromise resolution information by using a less bandwidth.